Assuming you mean the flickery shadow. If I recall correctly, this is a problem caused on later Windows versions.

Try to open the Setup, and enable "Triple Buffering" if it hasn't been yet (middle column right below the Mafia logo and Fullscreen checkbox). Alternatively, if that doesn't work, you might be able to force it on through your GPU control panel. Not sure about that though.

This setting is intended to prevent just that. Hopefully that fixes it for you. I don't seem to have this problem on my Windows 10, so it must be fixable._________________

For an immediate better understanding of the issue, it is recommended to provide details on the issue right away. Especially in this case with a heavily modified game, no one can point out what the issue is as we don't know what is supposed to work how.

I can't check the file at the moment, but from what I could hear in the video, I think I know the problem.
With Audacity, you can export 32bit Float WAV files and 16bit Signed WAV. I believe that Mafia does not like 32 bit WAV files and causes all sorts of varying issues with them. Try to export it to 16 bit._________________

In the video, the engine sound is clearly modified. Custom 3D models or textures should have no effect on audio. So any audio-related problems are 9/10 times directly related to the customized audio files in question._________________